The present invention relates generally to a ring type network system in such a mode that a plurality of physical links belonging to difference rings exists between two nodes opposite to each other, and more particularly to a ring type network system having a function of setting up a path (active path) capable of restraining use of standby resources for ring protection.
In a SONET (Synchronous Optical Network)/SDH (Synchronous Digital Hierarchy) network as a ring type network system, there is a method by which topology information is organized by advertising (broadcasting) virtual link information in a way that utilizes a routing protocol OSPF-TE (Open Shortest Path First-Traffic Engineering) (defined in RFC3630), and a path is set up based on a result of calculating a route of the path in a way that utilizes a signaling protocol RSVP-TE (Resource Reservation Protocol-Traffic Engineering) (defined in RFC3209, RFC3473) etc.
In the prior art, however, the ring information (ring configuration information) is not contained in the advertised virtual link information, and hence there is a case of taking a route coming and going between the plural rings. In this case, a standby path must be set up in each ring, and therefore such a problem arises that extra standby resources are needed.
For instance, as shown in FIG. 1, in a ring type network system SYS taking a mode wherein a plurality of physical links belonging to rings R1, R2 different from each other exists between two nodes N5, N6 opposite to each other, in the case of setting up a path (active path) AP extending from a node N1 to a node N4 configuring a first ring network NW1, a route of the path is calculated in the node N1. The topology information held by the node N1 does not contain ring information, and hence it is impossible to determine which link in the plurality of virtual links (TE links) between the node N6 and the node N5 is preferable for selection. Accordingly, there is a case of taking the route coming and going between the plural rings R1, R2.
In the case of UPSR (Unidirectional Path Switched Ring) ring as a first ring protection technology shown in FIG. 1, standby paths SP1, SP2, SP3 are set up in an opposite direction along a section extending from a point where a signal enters to a point where the signal exits, so that the extra standby resources are required in the case of the route coming and going between the rings R1, R2.
Further, in the case of BLSR (Bidirectional Line Switched Ring) ring as a second ring protection technology, on the route coming and going between the rings R1, R2, if a fault occurs in the node N5 or the node N6, resulting in a problem where the ring can not be restored.
The following is a related art to the present invention. [Patent document 1] Japanese Patent Laid-Open Publication No. 6-237262